The present disclosure is directed to multi-path cancellation in wireless communication and more specifically to accommodating for the multi-path interference.
Multi-path interference is an undesired phenomenon characteristic in the wireless communication field. In certain cases, it can produce serious communication channel impairment. It is characteristic to dense urban areas and confined areas such as shopping malls. One form of multi-path interference cancellation (MPIC) is suggested in “Channel Tracking for Rake Receivers in Closely Spaced Multipath Environments,” Fock et al., IEEE Journal on Selected Areas in Communications, vol. 19, no. 12, pp. 2420–31, December 2001. It uses fading coefficients and relative delays to compute a compensation term that allows cancellation of the effect of other paths on the timing error.
The present method extracts data from a received signal including multi-path interference in a rake receiver. The method includes sampling and filtering the received signal, estimating a time delay τl between paths for the filtered samples ψ(τ), and estimating channel complex coefficient cl for the filtered samples ψ(τ). Transmitted data x(τl) is extracted from the filtered samples ψ(τ) for each path l by solutions of simultaneous equations of the following filtered samples ψ(τ) equation:
            ψ      ⁡              (        τ        )              ⁢                  R        ff                  -          1                    ⁡              (                              τ            k                    -                                    τ              ^                        0                          )              ⁢                  Λ        ss        H            ⁡              (                              τ            ^                    k                )              =                    ∑                  l          =          0                          N                      p            -            1                              ⁢                          ⁢                                    c            l                    ⁡                      (                          τ              l                        )                          ⁢                  x          ⁡                      (                          τ              l                        )                          ⁢                              Λ            ss                    ⁡                      (                          τ              l                        )                          ⁢                              R            ff                    ⁡                      (                                          τ                l                            -                                                τ                  ^                                0                                      )                          ⁢                              R            ff                          -              1                                ⁡                      (                                          τ                k                            -                                                τ                  ^                                0                                      )                          ⁢                              Λ            ss            H                    ⁡                      (                                          τ                ^                            k                        )                                +                ⁢              (        τ        )            wherein k is a particular path, Np is the number of visible paths, Rƒƒ(τl–τo) is a double convolution matrix of the filtering process and Rƒƒ−1(τk–τo) is the pseudo inverse, Λss(τl) is the product of spreading and scrambling matrices and ΛssH(τk) is the inverse, and (τ) is noise.
The method is selectively performed for estimated time delay τl of a duration of one chip or less of the receiver. If the time delay is greater than one chip, no extraction is necessary. The filtered samples ψ(τ) equations without the noises (τ) are solved. The number of solutions may be less or equal to the number of over-samples per chip of the receiver. The solutions of the simultaneous equations may be stored in the receiver and the method performed in software.
These and other aspects of the present invention will become apparent from the following detailed description, when considered in conjunction with accompanying drawings.